Roller for hot rolling of wire rods and the like, and wire-rod and the like, hot-rolling machine provided with said roller

ABSTRACT

A wire-rod and the like, hot-rolling machine wherein the two rollers are fitted on respective frustoconical end portions of as many counter-rotating supporting shafts, via interposition of corresponding centering and coupling bushings having a frustoconical internal profile, each of which is fitted on the end portion of a respective supporting shaft, between the supporting shaft and the corresponding roller, and is structured so as to mesh on the supporting shaft so as to be angularly integral to said supporting shaft, and so as to be inserted/wedged between the supporting shaft and the roller thus to center the roller on the supporting shaft and moreover make the roller angularly integral to the body of the supporting shaft. Each centering and coupling bushing is provided with an annular flange having an eccentric lobe-shaped profile and which cantilevered projects from the outer surface of the bushing, at one of the two mouths of the central through hole of the roller, and is designed to engage a corresponding annular groove with eccentric lobe-shaped profile which is formed on the body of the roller at the mouth of the roller central through hole, and has a shape complementary to that of the annular flange.

TECHNICAL FIELD

The present invention relates to a roller for hot rolling of wire rodsand the like and to a wire-rod and the like, hot-rolling machineprovided with said roller.

More in detail, the present invention relates to a roller for hotrolling of concrete reinforcing bars and to a machine for hot rolling ofconcrete reinforcing bars. Use to which the following description willmake explicit reference, without this implying any loss of generality.

BACKGROUND ART

As is known, concrete reinforcing bars are obtained by subjecting asteel wire rod with a roughly circular cross section to a hot-rollingprocess that causes a progressive reduction of the nominal section ofthe wire rod.

The hot-rolling lines that are used for carrying out this particularmetallurgical process are usually formed by a fair number of rollingmachines, traditionally called “rolling stands”, which are arranged insuccession one after the other along the wire-rod feeding path so thateach rolling machine is able to cause a slight reduction of the nominalcross section of the wire rod while the latter advances along therolling line.

More in detail, each rolling machine is provided with: two opposed andcounter-rotating rollers, which are arranged in specular positions onopposite sides of the wire-rod feeding path, parallel and slightlyspaced apart to one another so as to delimit in between themselves aslot through which the wire rod to be hot-rolled is forced to pass; anda big electric or hydraulic motor able to drive the two rollers inrotation about their respective longitudinal reference axes at the samespeed of rotation.

Obviously, the width of the slot, i.e. the minimum distance between theperipheral surfaces of the rollers, progressively reduces along thewire-rod feeding path so that each pair of rollers is able to deform anddraw out the wire rod causing a slight reduction of the nominal sectionthereof.

In more recent rolling machines, in particular, the two rollers arerigidly fitted on the ends of two counter-rotating supporting shaftsthat are arranged in specular positions on opposite sides of thewire-rod feeding path, locally substantially perpendicular to thefeeding path itself, and are connected to the electric or hydraulicmotor via a gear train that enables the motor to drive the twosupporting shafts in rotation in mutually opposite directions, withidentical angular velocities.

To be able to withstand the mechanical and thermal stresses typical of ahot-rolling process, each roller instead usually consists of acylindrical-shaped monolithic block of tungsten carbide, which isprovided with a large central through hole dimensioned to enable thefitting/insertion of the roller on the end of the correspondingsupporting shaft.

Unfortunately, the tungsten carbide that is used for making the rollersis a very hard material resistant to abrasion, but is also extremelybrittle, so that the roller cannot be rigidly fitted on the supportingshaft via blocking pins, meshing between toothed sectors, or othersystems of interference fit, because use of these fitting systems wouldcause, during normal operation of the machine, formation of smallcrackings in the material that rapidly lead to breaking-up of theroller.

For this reason, in stands currently available on the market, fitting ofthe roller on the end of the supporting shaft is obtained by friction byinterposing between the roller and the supporting shaft a centring andcoupling bushing having a frustoconical internal profile and which isstructured so as to mesh on a toothed rim formed on the body of thesupporting shaft and simultaneously be force fitted/driven between theroller and a frustoconical portion of the supporting shaft so as to gripagainst the inner surface of the roller thus to keep the monolithicblock of tungsten carbide angularly integral to the body of thesupporting shaft.

Given that any sliding between the roller and the coupling bushing couldlead to the break of the roller, in order to prevent any sliding betweenthe roller and the blocking bushing, the centring and coupling bushingis moreover pressed/forced against the roller by a pack of suitablypre-loaded cup springs, which are fitted on the supporting shaft so asto be interposed between the annular rim of the centring bushing thatprotrudes from the hole of the roller and a big locknut that, in turn,is screwed directly on the end of the supporting shaft, beside theroller.

Obviously, by varying the distance between the bushing and the locknutit is possible to adjust the pre-load of the cup springs, and hence theforce applied on the centring and coupling bushing.

Unfortunately, the torque that is normally transmitted by the supportingshaft to the roller has very high values so that the cup springs mustexert on the centring and coupling bushing an extremely high axialthrust. Axial thrust that obviously must be countered by the locknut,with all the problems that this entails.

In rolling machines currently available on the market, in fact, thetightening torque that must be applied to the locknut can reach 40.000kgm, a value that can be reached only by screwing the locknut on the endportion of the supporting shaft with the aid of large hydraulic torquewrenches which, due to their weight and size, must be handled withextreme care. Consequently, the periodic replacement of the rollers ofan entire hot-rolling line becomes a particularly long and laboriousoperation that causes long machine downtimes, and has a significantincidence upon the costs of production of concrete reinforcing bars.

DISCLOSURE OF INVENTION

Aim of the present invention is to drastically reduce the times forroller replacement so as to increase the hour productivity of thehot-rolling line.

In compliance with the above aims, according to the present inventionthere is provided a wire rods and the like, hot-rolling machine asdefined in Claim 1 and preferably, though not necessarily, in any one ofthe claims depending thereon.

Moreover according to the present invention there is provided a rollerfor hot rolling of wire rods and the like as defined in Claim 14 andpreferably, though not necessarily, in any one of the claims dependingthereon.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to theannexed drawings, which illustrate a non-limiting example of embodimentthereof and in which:

FIG. 1 is a perspective view of a wire-rods and the like, hot-rollingmachine realized according to the teachings of the present invention;

FIG. 2 is a cross-sectional view of the top part of the wire-rods andthe like, hot-rolling machine shown in FIG. 1, with parts removed forclarity;

FIG. 3 is an exploded perspective view of the top part of the wire-rodsand the like, hot-rolling machine shown in FIG. 2, with parts removedfor clarity; and

FIG. 4 is a plan view of one of the rollers of the wire-rods and thelike, hot-rolling machine shown in FIGS. 1, 2, and 3.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIGS. 1, 2, and 3, number 1 designates as a whole amachine for hot rolling of wire rods and other similar semifinishedsteel products, which finds particularly advantageous use in theproduction of steel concrete reinforcing bars.

More in detail, the machine 1 is structured for hot rolling a wire rod 2or other similar semifinished steel product, that movers through themachine following a locally substantially rectilinear, feeding path p.

The wire-rods and the like, hot-rolling machine 1 basically comprises:an external supporting casing 3 which preferably, though notnecessarily, has a substantially parallelepipedal shape, and is locatedagainst the wire-rod feeding path p; and two rotating supporting shafts4, which are fixed/mounted in an axially rotatable manner in thesupporting casing 3 and cantilevered protrude from the supporting casing3 in substantially specular position on opposite sides of the wire-rodfeeding path p, while remaining locally parallel and facing to oneanother and substantially perpendicular to the wire-rod feeding path p,so as to arrange their respective ends portions 4 a in substantiallyspecular position on opposite sides of the wire-rod feeding path p.

In other words, the two supporting shafts 4 are placed on opposite sidesof the wire-rod feeding path p, with their respective referencelongitudinal axes A parallel and facing to one another and locallysubstantially perpendicular to the wire-rod feeding path p, so thattheir respective end portions 4 a are placed in substantially specularposition on opposite sides of the wire-rod feeding path p.

The two supporting shafts 4 are moreover able to rotate about theirrespective longitudinal reference axes A in mutually oppositedirections, substantially with identical angular velocities.

More in detail, the wire-rods and the like, hot-rolling machine 1 ispreferably provided with a gear train (not shown), which is housedwithin the supporting casing 3 and is structured so as to connect thetwo supporting shafts 4 to a same driving motor (not shown) preferably,though not necessarily, of an electric or hydraulic type, so as toenable said motor to drive in rotation the two supporting shafts 4simultaneously about their respective longitudinal reference axes A inmutually opposite directions, substantially with identical angularvelocities.

With reference to FIGS. 1, 2, and 3, the wire-rods and the like,hot-rolling machine 1 moreover comprises two opposed andcounter-rotating rollers 6 having a substantially cylindrical shape andwhich are provided with a central through hole 6 a, and arefitted/mortised each on the end portion 4 a of a respective supportingshaft 4 so that each of them is perfectly coaxial with the longitudinalaxis A of the corresponding supporting shaft 4.

The two rollers 6 are therefore placed, in specular positions, onopposite sides of the wire-rod feeding path p, locally substantiallyparallel to and facing one another and with their respectivelongitudinal axes locally substantially perpendicular to the wire-rodfeeding path p, and are moreover dimensioned to delimit, in betweenthemselves and at the wire-rod feeding path p, a slot within which thewire rod 2 to be hot-rolled is forced to pass.

More in detail, each roller 6 consists of a substantiallycylindrical-shaped, monolithic block 6 of tungsten carbide which isprovided with a substantially cylindrical-shaped, central through hole 6a which has a diameter such to enable the fitting of the monolithicblock 6 of tungsten carbide on the end portion 4 a of supporting shaft4.

With reference to FIGS. 2 and 3, in particular, the end portion 4 a ofeach supporting shaft 4 preferably presents a substantiallyfrustoconical profile converging towards the distal end of the sameshaft, and the wire-rods and the like, hot-rolling machine 1 alsocomprises two centring and coupling bushings 7 which preferably presenta frustoconical internal profile, and each of which is fitted on the endportion 4 a of a respective supporting shaft 4, between the supportingshaft 4 and the corresponding roller 6, and is structured so as todirectly mesh on the supporting shaft 4 so as to be angularly integralto the supporting shaft 4, and at same time so as to be inserted/wedgedbetween supporting shaft 4 and roller 6 so as to centre the roller 6 onthe supporting shaft 4 and in addition make the roller 6 angularlyintegral to the body of supporting shaft 4.

In the example shown, in particular, each supporting shaft 4 ispreferably provided with a protruding shank 4 b that cantileveredextends from the end portion 4 a of supporting shaft 4, while remainingperfectly coaxial to the longitudinal axis A of the same shaft, and eachcentring and coupling bushing 7 is structured so as to mesh on a toothedring 8 preferably with straight teeth, which is provided on the body ofsupporting shaft 4 roughly at the base of the projecting shank 4 b.

More in detail, in the example shown each centring and coupling bushing7 has an overall length greater than that of the end portion 4 a ofsupporting shaft 4 so as to cantilevered project from the roller 6towards the distal end of the supporting shaft 4 so as to surround/coveralso at least a part of the projecting shank 4 b, and is moreoverprovided, along the stretch of the central through hole that directlyfaces the projecting shank 4 b, with an internal toothed ring 9structured so to be able to mesh directly in the toothed ring 8 ofsupporting shaft 4.

In addition, the frustoconical internal part of the centring andcoupling bushing 7 preferably has a coning degree lower than that of thefrustoconical-shaped end portion 4 a of supporting shaft 4, in such away that the body of bushing 7 is forced to expand against roller 6 whenthe centring and coupling bushing 7 is force fitted/driven on the endportion 4 a of supporting shaft 4, causing the gripping of bushing 7against the inner surface of roller 6.

With reference to FIGS. 2, 3, and 4, each centring and coupling bushing7 is moreover provided with an annular flange 11 with an eccentriclobe-shaped profile, which cantilevered projects from the outercylindrical surface of the bushing 7 at one of the two mouths of thecentral through hole 6 a of the roller 6 (i.e. at one of the two basesof the roller 6), lies on a reference plane orthogonal to thelongitudinal axis of the centring and coupling bushing 7 (and hence alsolocally orthogonal to the longitudinal axis A of supporting shaft 4),and is designed to engage into a corresponding annular groove 6 b which,in turn, is formed on the body of roller 6 at the mouth of the centralthrough hole 6 a of the roller (i.e. directly on the base of the roller6), and has a shape complementary to that of the outer annular flange 11of bushing 7 so as to make the centring and coupling bushing 7 angularlyintegral to roller 6.

In other words, with reference to FIGS. 3 and 4, each roller 6 has, onthe base directly facing the annular flange 11, an annular groove 6 bwith eccentric lobe-shaped profile, which is formed in the body ofroller 6 at the mouth of the central through hole 6 a, and has a shapesubstantially complementary to that of the outer annular flange 11 ofthe centring and coupling bushing 7 so as to be engaged by the withlobe-shaped profiled, annular flange 11 of bushing 7.

In the example shown, in particular, the profile of the outer peripheraledge of the annular flange 11 of the centring and coupling bushing 7 ispreferably defined by a closed curved line that has a variable radius ofcurvature r which, for one or more stretches, is eccentric with respectto the longitudinal axis of bushing 7 (i.e. not intersecting it) which,in turn, coincides with the longitudinal axis A of supporting shaft 4.

Preferably, the annular flange 11 of the centring and coupling bushing 7is moreover shaped/profiled so that its barycentre is located on thelongitudinal axis of centring and coupling bushing 7, which in turncoincides with the longitudinal axis A of supporting shaft 4.

Likewise, the annular groove 6 b of roller 6 is preferablyshaped/profiled so that its barycentre is located on the longitudinalaxis of roller 6 which, in turn, coincides with the longitudinal axis Aof supporting shaft 4.

With reference to FIG. 4, similarly to the annular flange 11 of bushing7, in the example shown the profile of the outer peripheral edge of theannular groove 6 b formed on the base of roller 6, at the mouth of thecentral through hole 6 a of the same roller, is preferably defined by aclosed curved line that has a variable radius of curvature r which, forone or more stretches, is eccentric with respect to the longitudinalaxis of roller 6 (i.e. not intersecting it) which, in turn, coincideswith the longitudinal axis A of supporting shaft 4.

The profile of the outer peripheral edge of annular groove 6 b isfurthermore substantially identical to the profile of the outerperipheral edge of the annular flange 11 of centring and couplingbushing 7.

With reference to FIGS. 3 and 4, in the example shown, in particular,the annular flange 11 of the centring and coupling bushing 7 and theannular groove 6 b formed on the base of roller 6, have a substantiallyelliptical shape, with the two foci located, in specular position, onopposite sides respectively of the longitudinal axis of bushing 7 and ofthe longitudinal axis of roller 6, which in use coincide with thelongitudinal axis A of supporting shaft 4.

With reference to FIGS. 1, 2, and 3, the wire-rods and the like,hot-rolling machine 1 finally comprises, for each centring and couplingbushing 7, a respective removable blocking device 12 which is structuredto stably withhold the centring and coupling bushing 7 fitted/insertedon the end portion 4 a of supporting shaft 4, between supporting shaft 4and roller 6, with the outer annular flange 11 of bushing 7inserted/fitted in the annular groove 6 b of roller 6.

In the example shown, in particular, each blocking device 12 preferablycomprises: a lock nut 13 preferably substantially cup-shaped orbell-shaped, which is screwed directly on a threaded portion of thedistal end of supporting shaft 4, or rather of the projecting shank 4bof supporting shaft 4; and a pack of pre-compressed cup springs 14 orother similar elastic members, which are fitted on the distal end ofsupporting shaft 4, or rather on the projecting shank 4 b of supportingshaft 4, so as to be interposed between the body of lock nut 13 and thecentring and coupling bushing 7, so as to be able to press and withholdthe centring and coupling bushing 7 stably in abutment on roller 6, withthe outer annular flange 11 of bushing 7 fitted within the annulargroove 6 b of roller 6.

More in detail, with reference to FIG. 2, in the example shown the packof cup springs 14 is preferably fitted on the free end of the centringand coupling bushing 7, in abutment against a projecting annularshoulder 15 present on the outer surface of the bushing 7; whereas thecentral part of lock nut 13 is structured/shaped so to fit in telescopicmanner on the free end of bushing 7, thus to be able to arrive inabutment against the pack of cup springs 14 fitted on the same end ofthe bushing 7 and then compress the pack of cup springs 14 against theprojecting annular shoulder 15 of the centring and coupling bushing 7.

With reference to FIGS. 1, 2, and 3, preferably each blocking device 12is moreover provided with a substantially cylindrical protective sleeve16 which is shaped/structured so as to be fitted on supporting shaft 4,with the bottom annular rim 16 a of the sleeve in abutment against thebase of roller 6 where the annular groove 6 b is formed, and with thetop annular rim 16 b of the sleeve in abutment against the lock nut 13so as to surround and protect the pack of cup springs 14.

In other words, the protective sleeve 16 is shaped/structured so as tobe fitted on the portion of the bushing 7 that cantilevered projectsfrom roller 6 towards the distal end of supporting shaft 4, with thebottom annular rim 16 a of the sleeve in abutment on the base of roller6 where the annular groove 6 b is formed, and with the top annular rim16 b of the sleeve in abutment against the lock nut 13.

More in detail, in the example shown, the protective sleeve 16 ispreferably shaped/structured so as to bring the bottom annular rim 16 aof the sleeve in abutment on the base of roller 6, outside of theannular groove 6 b, so as to surround and cover the coupling areabetween centring and coupling bushing 7 and roller 6.

The top annular rim 16 b of sleeve 16 is, instead, preferably shaped soas to be able to couple with the perimetral edge of lock nut 13substantially for the whole length, so as to cover and protect the packof cup springs 14 fitted on the free end of centring and couplingbushing 7.

In addition, sleeve 16 is preferably also shaped/structured so as to beable to mesh directly on the portion of bushing 7 that cantileveredprojects outside of roller 6, so as to be angularly integral to thecentring and coupling bushing 7.

In the example shown, in particular, sleeve 16 is preferably structuredso as to be able to mesh on a toothed ring 17 preferably with straightteeth, which is provided on the outer surface of bushing 7, between theouter annular flange 11 of bushing 7 and the annular shoulder 15.

More in detail, in the example shown sleeve 16 has, along a stretch ofits central through hole, an internal toothed ring 18 which isstructured so as to be able to mesh directly in the toothed ring 17 ofcentring and coupling bushing 7.

With reference to FIG. 2, preferably the wire-rods and the like,hot-rolling machine 1 finally comprises, along each supporting shaft 4,an annular thrust-bearing element 20 which is fitted on the stretch ofsupporting shaft 4 immediately adjacent to the end portion 4 a ofsupporting shaft 4, without possibility of further axial displacementalong the same supporting shaft 4, so as to abut against the base ofroller 6 without the annular groove 6 b, and prevent the roller 6 frommisalign with respect to the frustoconical end portion 4 a of supportingshaft 4.

In other words, the annular thrust-bearing element 20 is fitted on thesupporting shaft 4 beside the roller 6 and the centring and couplingbushing 7, on the opposite side with respect to the projecting shank 4b, with no possibility of displacing along the supporting shaft 4 in adirection opposite to the end portion 4 a, so as to support and hold theroller 6 in place on the frustoconical end portion 4 a of supportingshaft 4.

Operation of the wire-rods and the like, hot-rolling machine 1 is easilyinferable from the foregoing description and hence does not require anyfurther explanation.

As regards, instead, the coupling between roller 6 and centring andcoupling bushing 7, experimental tests have revealed that the particularshape of the outer annular flange 11 of centring and coupling bushing 7and of the annular groove 6 b present on the base of roller 6, allows tokeep the roller 6 angularly integral to the centring and couplingbushing 7, without the mechanical stresses generated between the twocomponents during normal operation of the machine 1 to cause, in thematerial that forms the roller 6, cracks that might lead to breaking-upof roller 6.

The advantages deriving from the particular structure of the roller 6and of the centring and coupling bushing 7 are considerable.

The two blocking devices 12, in fact, now simply have to withhold thetwo centring and coupling bushings 7 in place without any need to exertparticularly high axial thrusts, because the blocking of the roller onthe centring and coupling bushing 7 is no longer obtained by friction.

Consequently, the tightening torque to be applied on the lock nuts 13has values that are lower, by at least two orders of magnitude, thanthose required by current systems for blocking rollers and can be easilyreached using normal wrenches.

This possibility renders superfluous the use of hydraulic torquewrenches and enables drastic reduction of the times for replacement ofthe rollers, thus enormously simplifying the operations of maintenanceof the hot-rolling line.

It is finally apparent that changes and variants can be made to theabove-described, wire-rods and the like, hot-rolling machine 1 and tothe roller 6 described herein, without departing from the scope of thepresent invention.

For example, in a different, less sophisticated embodiment, the blockingdevice 12 may comprise: a cup-shaped body structured/shaped so to befitted directly on the distal end of supporting shaft 4, or rather onthe projecting shank 4 b of supporting shaft 4, and so as to arrange itsperimetrical rim in abutment against the base of roller 6 where theannular groove 6 b is provided, outside the same annular groove 6 b; andone or more anchoring bolts that engage in pass-through manner thebottom of the cup-shaped body and then are screwed in the body ofsupporting shaft 4, or rather in the projecting shank 4 b of supportingshaft 4, so as to rigidly block the cup-shaped body on the distal end ofsupporting shaft 4, or rather on the projecting shank 4 b of supportingshaft 4.

In another embodiment, moreover, roller 6, instead of being made oftungsten carbide, could also consist in a monolithic block 6 ofhigh-resistance cast iron or special steel, once again substantiallycylindrical-shaped and once more provided with a cylindrical-shaped,central through hole 6 a with a diameter such as to enable the fittingof the monolithic block of cast iron on the frustoconical end portion 4a of supporting shaft 4.

1. Wire-rod and the like, hot-rolling machine which is adapted to hot-roll a wire-rod or the like moving forward along a pre-established feeding path, and which comprises: two counter-rotating supporting shafts which are arranged on opposite sides of the wire-rod feeding path, with respective longitudinal axes parallel to and facing each other and locally substantially perpendicular to the wire-rod feeding path, so as to arrange respective end portions in a substantially specular position on opposite sides of the wire-rod feeding path; two rollers which are provided with a central through hole and are each fitted onto a respective supporting shaft, at the end portion of said supporting shaft; and two centering and coupling bushings, each of which is fitted on the end portion of a respective supporting shaft, between the supporting shaft and the corresponding roller, and is structured so as to mesh on the supporting shaft to be angularly integral to said supporting shaft, and so as to be inserted/wedged between the supporting shaft and the roller, thus to center the roller on the supporting shaft and also to make the roller angularly integral to the body of the supporting shaft; wherein each centering and coupling bushing is provided with an annular flange having eccentric lobe-shaped profile and which cantilevered projects from the outer surface of the bushing at one of the two mouths of the central through hole of the roller, and wherein each roller has, on the base facing the annular flange of the bushing, a corresponding annular groove which is formed on the body of the roller so as to surround the mouth of the central through hole of the roller, and has an eccentric lobe-shaped profile which is complementary in shape to that of the annular flange of the centering and coupling bushing so as to be engaged by the annular flange of said bushing.
 2. Machine according to claim 1, wherein the profile of the outer peripheral edge of the annular flange of the centering and coupling bushing is defined by a closed curved line that has a variable radius of curvature which, for one or more stretches, is eccentric with respect to the longitudinal axis of the bushing.
 3. Machine according to claim 1, wherein the profile of the outer peripheral edge of the annular groove of the roller is defined by a closed curved line that has a variable radius of curvature which, for one or more stretches, is eccentric with respect to the longitudinal axis of the roller.
 4. Machine according to claim 3, wherein the profile of the outer peripheral edge of the annular groove is substantially identical to the profile of the outer peripheral edge of the annular flange of the centering and coupling bushing.
 5. Machine according to claim 1, wherein the end portions of the two supporting shafts have a substantially frustoconical profile, and in that the two centering and coupling bushings present on the inside a frustoconical profile.
 6. Machine according to claim 1, wherein the annular flange of the centering and coupling bushing is shaped/profiled so as to have its bary center located on the longitudinal axis of the centering and coupling bushing.
 7. Machine according to claim 1, wherein the annular groove of the roller is preferably shaped/profiled so as to have its bary center located on the longitudinal axis of the roller.
 8. Machine according to claim 1, wherein the annular flange of the centering and coupling bushing and the annular groove of the roller are substantially elliptical in shape.
 9. Machine according to claim 1, further comprising an external supporting casing which is located against the wire-rod feeding path; the two supporting shafts being mounted in an axially rotatable manner on the supporting casing so as to cantilevered project from the supporting casing in substantially specular position, on opposite sides of the wire-rod feeding path, thus to arrange the respective end portions in a substantially specular position on opposite sides of the wire-rod feeding path.
 10. Machine according to claim 9, further comprising a gear train which is housed within the supporting casing and is structured so as to connect the two supporting shafts to a same driving motor, so as to allow said motor to drive the two supporting shafts simultaneously in rotation about their respective longitudinal axes in mutually opposite directions, substantially with identical angular velocities.
 11. Machine according to claim 1, further comprising, for each centering and coupling bushing, a respective removable blocking device which is structured so as to withhold the centering and coupling bushing stably fitted/inserted on the end portion of the supporting shaft, between the supporting shaft and the roller, with the annular flange of the bushing inserted/fitted in the annular groove of the roller.
 12. Machine according to claim 11, wherein the removable blocking device comprises a lock nut which is screwed directly on the distal end of the supporting shaft, and elastic means which are fitted on the distal end of the supporting shaft so as to be interposed between the body of the lock nut and the centering and coupling bushing, thus to press and withhold the centering and coupling bushing stably in abutment against the roller.
 13. Machine according to claim 1, wherein each roller consists of a substantially cylindrical-shaped, monolithic block of tungsten carbide which is provided with a central through hole with a diameter such as to allow the fitting of the monolithic block of tungsten carbide on the end portion of the supporting shaft.
 14. Roller for hot rolling of wire rods and the like, comprising a substantially cylindrical-shaped, monolithic block of high-resistance material which is provided with a central through hole designed to allow the fitting of the monolithic block of high-resistance material on a supporting shaft; wherein said monolithic block of high-resistance material has, on one of its two bases, an annular groove which is formed on the body of the monolithic block of high-resistance material so as to surround the mouth of the central through hole, and has an eccentric lobe-shaped profile.
 15. Roller according to claim 14, wherein the profile of the outer peripheral edge of the annular groove of the monolithic block of high-resistance material is defined by a closed curved line having a variable radius of curvature which, for one or more stretches, is eccentric with respect to the longitudinal axis of the monolithic block of high-resistance material.
 16. Roller according to claim 14, wherein the annular groove with eccentric lobe-shaped profile is substantially elliptical in shape.
 17. Roller according to claim 16, wherein the two foci of the ellipse are located, in specular position, on opposite sides of the longitudinal axis of the monolithic block of high-resistance material.
 18. Roller according to claim 14, wherein the monolithic block of high-resistance material is a substantially cylindrical-shaped, monolithic block of tungsten carbide. 